Folding escape ladders for multistoried buildings have been known for many years. Typically, folding escape ladders are comprised of a fixed rail attached to the side of the building and a movable rail attached to the fixed rail by a plurality of spaced rungs, the rungs pivotally attached so that the ladder can be folded up against the building. However, to be of practical use, particularly for buildings of more than a few storeys, designs for folding ladders need to provide a release mechanism to deploy the movable rail so that the rungs become horizontal and the ladder useable. The release mechanism should be operable from any floor and should deploy the entire ladder. Further, some means must be provided to prevent the movable rail from continuing to move downward after the rungs become horizontal so that once the rungs become horizontal, the ladder provides a firm and stable means of escape. The ladder should not depend upon the ground or some other surface for support (which could shift or give way), but should be self-supporting, relying only upon the building wall for support. Further, for large buildings it is essential that an escape ladder be capable of distributing weight over the entire ladder structure so as not to risk failure of the ladder by concentrating the weight in any particular portion of the structure.
One of the first folding escape ladders is Miller, U.S. Pat. No. 295,127 (Mar. 11, 1884), in which the release mechanism is a cable actuated by a lockable lever near the ground and the lower end of the movable rail rests upon the ground when the ladder is deployed. Disadvantages of the Miller, U.S. Pat. No. 295,127, design are that only someone at ground level with a key may deploy the ladder and that as the rungs are not individually secured against pivoting beyond a horizontal position, the ladder may be somewhat rickety.
Bracklo, U.S. Pat. No. 719,990 (Feb. 10, 1903) appears to improve upon the ladder disclosed in Miller, U.S. Pat. No. 295,127, by providing for release by a cord that may be cut at any window and by increasing rigidity by providing the rungs d with cam-heads d.sup.2. Each rung d appears to support itself when the ladder is deployed as each cam-head d.sup.2 presses against the side of a building. Disadvantages of the Bracklo, U.S. Pat. No. 719,990, design are (1) that an unauthorized person at ground level could apparently deploy the ladder by cutting the cord and (2) as the ladder as a whole is held by the cord, the release of the ladder would take place with considerable force as no means is provided to slow the fall of the ladder into deployed position, possibly damaging the ladder or injuring bystanders.
Padlo, U.S. Pat. No. 2,957,539 (Oct. 25, 1960) discloses a folding escape ladder for small size building having release mechanisms (FIG. 5) inside the building for releasing the ladder. A hydraulic cylinder 45 is provided to slow the release of the ladder 10. The lower end 18 of the movable rail 12 rests upon the ground G when the ladder 10 is deployed. A side brace 50 shown in FIG. 3 is provided to stabilize the ladder 10.
Padlo, U.S. Pat. No. 3,024,864 (Mar. 13, 1962) discloses a folding ladder in which the rungs nest inside each other.
Wedvik, U.S. Pat. No. 3,414,081 (Dec. 3, 1968) discloses a contractible ladder apparently suitable for a two storey building that does not need support from the ground when deployed. Instead, stops 30 on the ends of the rungs 18 provide stiffening of the ladder by bearing against the legs 10, 12 when the ladder is deployed. A single lever 38 deploys the ladder.
Reinhard, U.S. Pat. No. 3,575,263 (Apr. 20, 1971) discloses a folding fire escape ladder. Each rung 21 is stiffened by stop rivets 34 and 38.
Messera et al., U.S. Pat. No. 3,756,347 (Sep. 4, 1973) discloses an emergency escape ladder. A lifting bar 52 is used to deploy the ladder by lifting hook 58 out of hole 62. The lifting bar 52 and flange 30 are each provided with cam wedges 76 and 78, respectively, which urge the lower end of the moveable subassembly 14 away from the stationary sub-assembly 12 when the lifting bar 52 is raised. If the moveable subassembly 14 does not rest upon the ground or some other surface when the ladder is deployed, then it appears that the moveable subassembly 14 is restrained from movement beyond the desired deployed position entirely by the bottom rung 24 bearing against notch 80.
Shull, U.S. Pat. No. 4,037,686 (Jul. 26, 1977) discloses an escape ladder formed of channel-shaped pieces, the cross-members 45 folding inside of and hinged to the side pieces 15, 16 so that the ends of the cross-members 45 abut the insides of the side pieces 15, 16 in deployed position.
Reinhard, U.S. Pat. No. 4,189,028 (Feb. 19, 1980) discloses a folding fire escape ladder generally similar to Reinhard, U.S. Pat. No. 3,575,263. Stop pins 27, 33 are provided to limit movement of the rungs 16.
Rossey, Sr., U.S. Pat. No. 4,243,119 (Jan. 6, 1981) discloses a folding building side mounted fire ladder having an articulated brace 40 between the upper ends of the side rails 26, 28. No means are provided to stiffen the individual rungs 30.
Reinhard, U.S. Pat. No. 4,425,983 (Jan. 17, 1984) discloses a folding fire escape ladder generally similar to Reinhard, U.S. Pat. No. 4,189,028 (Feb. 19, 1980) and Reinhard, U.S. Pat. No. 3,575,263.
Grin, U.S. Pat. No. 4,463,829 (Aug. 7, 1984) discloses a portable foldable ladder. A locking mechanism (FIGS. 6-8) stabilizes the ladder when in an open mode as latch 62 engages catch plate 72.
Pugliese, U.S. Pat. No. 4,678,060 (Jul. 7, 1987) discloses a collapsible ladder device. Rungs 20 are restrained from swinging past their horizontal positions as the ladder is deployed by the expedient of mounting bracket members 22-28, which are located at the ends of the rungs 20 on pins 29 that are located off-center so that brackets 22-28 engage the bottom wall of the channels 16, 18, limiting the rotational motion of the brackets.
Nilsen, U.S. Pat. No. 4,702,347 (Oct. 27, 1987) discloses a folding fire escape ladder with separate release stations and safety belts with locking brackets. The ladder disclosed is composed of sections that link together to form an escape ladder for a multi-floor building. As each section is deployed, the sections below (but not above) are also deployed.
Soucy, U.S. Pat. No. 4,245,717 (Jan. 20, 1981) discloses a fire escape ladder having support braces, one end of which pivots from the inner end of one rung and the other end of which slides along the rung above as the ladder is opened.
Byrnes, Jr., U.S. Pat. No. 4,805,736 (Feb. 21, 1989) discloses a disappearing ladder the opening of which is actuated by a rod which rotates the rungs of the ladder about their longitudinal axes. Eriksson, U.S. Pat. No. 5,339,920 (Aug. 23, 1994) discloses a foldable fire-escape ladder. Each rung pivots on axes that are centered off the center line of the rung, thereby apparently improving the stability of the ladder.
Of the ladders disclosed in the patents discussed above none seem suitable for multistoried buildings of more than a few storeys.